IGNITION
90-883728 JULY 2001 Page 2A-23
Symptom Cause Action
3. Engine idle is rough 3.1 Fouled spark plug Replace spark plug: if carbon
bridges electrode gap or if it is
completely black. If it is not firing
and is wet with fuel.
Note: If spark plug is grey or com-
pletely black with aluminum specs,
this indicates a scuffed piston.
3.2 Failed fuel injector Refer to specifications for ohm
test.
3.3 Bad coil/weak spark Refer to specifications for ohm
test.
3.4 Flywheel misaligned during
installation
Remove flywheel and inspect.
4. Engine idles fast (rpm
>700) or surges
4.1 Fuel leak Check for fuel entering induction
manifold.
Fuel pump diaphragm leaking and/
or Vapor Separator flooding over.
4.2 Improper set-up Check throttle cable & cam roller
adjustment.
5. Engine runs rough below
3000 rpm
5.1 Fouled spark plug See 3.1
5.2 Throttle misadjusted Check throttle cam setup on induc-
tion manifold. Inspect linkage and
roller.
If throttle plate stop screws have
been tampered with, contact Mer-
cury Marine Service Department
for correct adjustment procedures.
5.3 Bad coil/weak spark See 3.3
5.4 TPS malfunction See 2.2
6. Engine runs rough above
3000 rpm
6.1 Fouled spark plug See 3.1
6.2 Speed Reduction See 7
6.4 TPS malfunction See 2.2
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